Relationship between serum bactericidal activity and serogroup-specific immunoglobulin G concentration for adults, toddlers, and infants immunized with Neissaria meningitidis serogroup C vaccines

A new meningococcal group C-CRM197 conjugate vaccine (MnCC; Meningitec) has been evaluated in multiple clinical trials in the United States and most r ecently has been approved for routine administration in the United Kingdom. Meningococcal serogroup C (MnC)-specific immunoglobulin G (IgG) antibodies in pre-and postimmunization sera obtained from healthy U.S, adults, toddle rs, and infants were quantitated by enzyme-linked immunosorbent assay (ELIS A) and by an antibody dependent, complement-mediated serum bactericidal ass ay (SBA), Serogroup-specific IgG antibody (micrograms per milliliter) in ad ults immunized either with the quadrivalent polysaccharide (A, C, Y, and W- 135) vaccine or with MnCC showed a strong correlation (r = 0.848 and 0.934, respectively) by linear regression analysis with SEA. Sera from infants im munized with the MnCC (n = 30) and an age matched unimmunized control group (n = 15) were also analyzed. Linear regression analysis of serum bacterici dal and IgG ELISA data from sera obtained at 2 months of age (preimmunizati on) shelved no correlation; however, a high degree of correlation was obser ved at time points after two (r = 0.877) and three (r = 0.951) immunization s, where significant rises in anti-MnC polysaccharide antibodies occurred r elative to the age-matched control group. Infants previously primed with 3 doses of MnCC were given a booster dose of conjugate vaccine at 12 to 15 mo nths of age. The correlation coefficient of ELISA to SEA for combined pre- and postbooster data was r = 0.836 (11 = 48 pairs). In conclusion, increase s in serum bactericidal activity in immunized adult, toddler, and infant po pulations were found to correlate very well with increases in serogroup-spe cific IgG concentrations, whereas the correlation between these two assays in nonimmunized 2-month-old infants was poor. Characterizing the relationsh ip between these methods is important for understanding the significance of antigen-specific antibody concentrations relative to vaccine performance a nd protection from disease.